Signal transduction pathways play important roles in cellular responses to ionizing radiation. We have recently observed that one of these pathways, that involving the transcriptional factor NF-kappaB, is implicated in the extreme radiation sensitivity of cells from patients with the human genetic disease, ataxia telangiectasia (AT). Furthermore, preliminary experiments with human squamous carcinoma cells (SCCs) reveal that components of the NF-kappaB/IkappaB complex are expressed at various levels, and show evidence of differences in message size. Since these cell lines have been previously characterized to show various intrinsic radiation sensitivities, we propose to investigate NF-kappaB function in these radiation sensitive and radiation resistant human tumor cells (SCCs). We will test the hypothesis that impaired NF-kappaB regulation results in a more radiation sensitive cellular phenotype. Using a model cell system of three radiation sensitive and three radiation resistant SCCs, we will measure expression levels and structural integrities of genes coding for components of the NF-kappaB/IkappaB complex. DNA-protein binding assays, and reporter gene expression assays will determine whether radiation resistant cells can be made more sensitive in their response to ionizing radiation by interfering with the NF-kappaB signaling pathways. The completion of the experiments in this proposal will provide insight into the NF-kappaB pathway and its relationship to cellular radiation response. Such knowledge may identify useful molecular information for application in diagnostic and therapeutic strategies to improve the cancer treatment therapeutic ratio.